DE 199 43 689 A1 discloses a method and an apparatus for monitoring and/or diagnosis of moving machines and/or machine parts. The aim of such measurement and evaluation methods is to identify damage to a machine or to a machine part such as a roller bearing as early as possible in order to make it possible to replace this item, when appropriate, before its total failure.
In this known method, oscillations and structure-borne sound waves which are produced by the machines or machine parts are recorded by means of an acceleration sensor as a broadband time signal, and are passed to an evaluation device. The measurement signal is digitized in this evaluation device, and a relatively large range of such digital values are stored. This data is subjected to frequency analysis by means of a fast Fourier transformation in a subsequent calculation process. The process of carrying out a fast Fourier transformation such as this is highly complex and requires a comparatively large amount of computation capacity and memory space.
Furthermore, this document discloses the broadband time signal being subjected to discrete filtering using different analysis methods.
During this process, frequency components of the signal components caused by the damage are filtered out from the measurement signal, and an amplitude profile of this component is evaluated. Changes in the frequencies can extend the evaluation to adjacent signal components in such a way that the local amplitude maxima can be determined. The computation complexity for carrying out discrete filtering is admittedly less than that of such a conventional Fourier transformation, but it is nevertheless comparatively high since the cut-off frequencies of the filter must be dynamically matched to different rotation speeds of the shaft/bearing system.
Finally, DE 101 36 438 A1 discloses a sensor arrangement in which strain gauges are arranged in a circumferential groove in a stationary roller bearing ring, where they are connected to signal-electronic modules, by means of which a signal evaluation process can be carried out directly in the circumferential groove in the roller bearing ring. Since this circumferential groove is comparatively small, the signal-electronic modules which are arranged there may have only a quite modest storage and computation capacity, so that the evaluation methods described above are not carried out in situ and, so to speak “on-line”.